Abstract
The ultrastructural changes of phloem parenchyma cells of tomato plants affected by yellow leaf curl disease are described. The nuclei were severely altered, the chromatin was reduced to a few peripheral clumps and the nucleoplasm contained ring-like electron opaque structures and massive aggregates of virus-like particles. These particles were rounded, measured 15 to 17 nm in diam. and occasionally appeared to occur in pairs. Based on these findings, the presence of a geminivirus in the tomato tissues examined is inferred.